1. Field of the Invention
The present invention relates to reducing bandwidth limited noise in an optical scanner; in particular, in a bar code scanner.
2. Description of the Related Art
U.S. Pat. No. 5,852,286, which issued to Ed Coleman, and which is assigned to PSC Inc., and which is incorporated in its entirety herein by reference, discloses a system and method for reducing bandwidth limited noise in a bar code scanning system. FIGS. 1 through 10 provide details of such a system and method. In such a system and method, a duty cycle of a laser light source is controlled such that it repeatedly is "on" for a certain period of time, and then "off" for a certain period of time. Furthermore, positive and negative gains of a demodulator circuit at a receive side are controlled in accordance with the duty cycle. As a result, the elements of a received signal that are contributed by the ambient light are substantially canceled out.
Thus, the system and method described above reduces bandwidth limited noise by modulating the light and then synchronously controlling the demodulation in the signal processing of the photodetector signal. Also, the duty cycle of the pulsing can be varied, along with the gains in the demodulation portion.
While the system and method described above is useful for reducing the noise caused by ambient light, such a system and method may not be so useful when other optical scanners are utilized in a same environment, for systems that do not operate in a pulsed manner, or for systems operating in an environment where the ambient light characteristics are unknown or varying.